While barcodes are a common means for encoding information in printed material, they can be obvious and are often unattractive. Therefore, if an image is to be a part of the composition of a printed label or page, a method of hiding information within the image may be used as an alternative to barcoding. Information may be encoded in the halftone of an image, using techniques such as clustered-dot halftoning. The process takes any grayscale image and a payload of data to be encoded therein as input, and produces a bitonal clustered-dot halftone of that image with selected halftone clusters shifted to carry varying numbers of bits from the payload. The small size and large number of clustered-dot cells in printed halftones allow the printer/encoded bit density to be quite high, typically over 2000 bytes/square-inch. The result of this encoding process is a data-bearing steganographic halftone, or stegatone.
Stegatones are used to convey digital information through a printing-imaging cycle via manipulating the halftone structure associated with a given image, or carrier. In order to extract this information from the halftone while maintaining maximum storage efficiency of the carrier, it is necessary to align a printed, imaged carrier with a reference halftone image created in the process of printing the carrier. However, proper alignment of the carrier stegatone with the reference halftone may present a challenge, making it difficult to effectively decode data-bearing images.